U.S. patent number 4,442,169 [Application Number 06/343,545] was granted by the patent office on 1984-04-10 for multiple coated cutting tool and method for producing same.
This patent grant is currently assigned to General Electric Company. Invention is credited to Donald E. Graham.
United States Patent |
4,442,169 |
Graham |
April 10, 1984 |
Multiple coated cutting tool and method for producing same
Abstract
An article of manufacture adapted for use as a cutting tool is
provided with an aluminum oxide coated substrate having layers of
TiN and/or TiC deposited thereon, whereby the beneficial
characteristics of the TiN, TiC and Al.sub.2 O.sub.3 coatings are
provided simultaneously for such cutting tool. The TiN/TiC outer
layers are strongly bonded to the Al.sub.2 O.sub.3 layer by means
of an intermediate TiO layer. The process for producing such insert
is also disclosed.
Inventors: |
Graham; Donald E. (St. Clair
Shores, MI) |
Assignee: |
General Electric Company
(Schnectady, NY)
|
Family
ID: |
23346556 |
Appl.
No.: |
06/343,545 |
Filed: |
January 28, 1982 |
Current U.S.
Class: |
428/332; 148/237;
427/253; 428/336; 428/698; 427/249.19; 148/220; 148/278; 427/287;
428/472; 428/701 |
Current CPC
Class: |
C23C
30/005 (20130101); Y10T 428/26 (20150115); Y10T
428/265 (20150115) |
Current International
Class: |
C23C
30/00 (20060101); B32B 015/04 () |
Field of
Search: |
;428/332,336,457,548,217,472,701,698 ;427/249,253,250,287
;148/6.3,16.6,16.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Herbert, Jr.; Thomas J.
Attorney, Agent or Firm: Hedman, Gibson, Costigan &
Hoare
Claims
What is claimed is:
1. An article comprising:
(i) a cemented carbide or aluminum base solid ceramic substrate
having aluminum oxide on at least portions of the surface thereof,
said aluminum oxide forming a first surface;
(ii) an intermediate layer of an oxide of titanium adjacent at
least a portion of said first surface; and
(iii) an outer layer of at least one of titanium nitride, titanium
carbide and titanium carbonitride adjacent at least a portion of
said intermediate layer.
2. The article as defined in claim 1 wherein said intermediate
layer contains TiO.
3. The article as defined in claim 2 wherein said intermediate
layer is less than or equal to approximately 1 micron in
thickness.
4. An article as defined in any one of claims 1, 2 and 3 wherein
said outer layer includes sub-layers of titanium nitride and
titanium carbide, said titanium carbide sub-layer being disposed
between and adjacent to said titanium nitride sub-layer and said
intermediate layer.
5. An article comprising:
(i) a cemented carbide or aluminum base solid ceramic substrate
having aluminum oxide on at least portions of the surface thereof,
said aluminum oxide forming a first surface;
(ii) an intermediate layer of an oxide of titanium adjacent at
least a portion of said first surface; and
(iii) an outer layer of at least one of titanium nitride, titanium
carbide and titanium carbonitride adjacent at least a portion of
said intermediate layer, said outer layer further including
sub-layers of titanium nitride and titanium carbide, said titanium
carbide sub-layer being disposed between and adjacent to said
titanium nitride sub-layer and said intermediate layer.
6. The article as defined in claim 5 wherein said intermediate
layer contains TiO.
7. The article as defined in claim 6 wherein said intermediate
layer is less than or equal to approximately one micron in
thickness.
8. A process for coating at least portions of a cemented carbide or
aluminum base solid ceramic substrate having aluminum oxide on at
least portions of the surface thereof with an outer layer of at
least one of titanium carbide, titanium nitride and titanium
carbonitride, comprising:
depositing a layer of TiO.sub.2 on said substrate adjacent said
aluminum oxide by first heating said substrate, passing a gaseous
mixture of hydrogen and titanium tetrachloride over the surface of
said substrate, and finally introducing up to 15% by volume of
CO.sub.2 along with hydrogen and titanium tetrachloride;
reducing at least a portion of said TiO.sub.2 to TiO to form an
intermediate layer by passing only hydrogen and titanium
tetrachloride over the surface of said substrate; and
depositing said outer layer adjacent to said intermediate layer by
introducing methane, nitrogen, or both, respectively, along with
hydrogen and titanium tetrachloride.
9. The process as defined in claim 8 wherein said step of
depositing a layer of TiO.sub.2 includes heating said substrate at
approximately 1050.degree.-1100.degree. C., passing a gaseous
mixture of hydrogen and titanium tetrachloride over the surface of
the substrate for 0-5 minutes, and introducing up to 15% by volume
of CO.sub.2 along with hydrogen and titanium tetrachloride for
approximately 1-35 minutes.
10. The process as defined in claim 9 wherein the step of reducing
includes passing only hydrogen and titanium tetrachloride over the
surface of the substrate for a period of up to approximately 30
minutes at a temperature of about 1000.degree. C.
11. The process as defined in claim 10 wherein the final step of
depositing includes passing nitrogen, hydrogen and titanium
tetrachloride over the surface of the substrate to form titanium
nitride.
12. The process as defined in claim 10 wherein the final step of
depositing includes passing methane, hydrogen and titanium
tetrachloride over the surface of the substrate to produce titanium
carbide.
13. The process as defined in claim 10 wherein the final step of
depositing includes passing nitrogen, methane, hydrogen and
titanium tetrachloride over the surface of the substrate to thereby
produce titanium carbonitride.
Description
BACKGROUND OF THE INVENTION
The present invention is directed to cemented carbide cutting
inserts having chemical vapor deposited coatings thereon for
increasing the wear resistance of the cutting inserts.
Use of chemical vapor deposited (CVD) coatings on a carbide cutting
tool, such as WC-Co or WC-TiC-TaC-Co cutting tools to increase the
wear resistance of such cutting tools is well known. The improved
performance is a result of chemical stability, refractory
characteristics, hardness and a low coefficient of friction
inherent in such coatings.
TiN, TiC and Al.sub.2 O.sub.3 are examples of such coatings. Each
of these coatings exhibits the above described properties in
varying degrees and ranges such that no one coating, by itself,
performs optimally over the wide range of cutting conditions
employed by industry. For example, Al.sub.2 O.sub.3 coatings are
superior to the other coatings at high cutting speeds where high
temperatures are encountered, because of the very high chemical
stability and low thermal conductivity which are properties of the
ceramic. On the other hand, at very low speeds where metal buildup
often causes tool failure, there are indications that TiN coatings
are superior to others because of their low coefficient of
friction. Further, the combination of hardness and chemical
stability inherent in TiC makes it the optimum coating over a very
broad range of intermediate speeds. Clearly, a cutting insert
having the properties of two or more of such coatings would provide
a highly useful tool capable of operating over a wide range of
conditions.
A straightforward approach to the foregoing problem would be to
provide a multi-layer coating on the cemented carbide cutting tool,
the coating consisting of two or more of the above described
coatings. However, the major difficulty in producing such a cutting
tool is in obtaining sufficient adherency between coating layers,
especially between the ceramic Al.sub.2 O.sub.3 and the other
coatings.
Various prior art cutting tools employ adjacent layers of Al.sub.2
O.sub.3 and TiN or TiC on a cemented carbide substrate. Two such
tools are disclosed in U.S. Pat. Nos. 3,837,896 and 3,955,038 both
on Lindstrom et al. Disclosed therein are cutting tools comprised
of a cemented carbide substrate and a thin coating layer of
Al.sub.2 O.sub.3. A diffusion barrier layer is stated to be
required between the Al.sub.2 O.sub.3 layer and the carbide
substrate due to the harmful catalyzing effect in the formation and
growth of the oxide layer due to Co and/or C in the carbide
substrate. Such barrier layer may consist of nitrides or carbides
of titanium.
Another insert disclosed in U.S. Pat. No. 4,150,195 to Tobioka et
al employs a multi-layer coating deposited upon a carbide
substrate. The multi-layer coating may include aluminum oxide as
the most exterior layer, titanium carbonitride for the most
interior coating layer, and titanium oxycarbonitride as an
intermediate layer between the aluminum oxide and titanium
carbonitride layers. The stated use of the intermediate layer of
titanium oxycarbonitride is to increase the adhesive strength of
the multi-layer coating.
None of the above cutting tools employ such multi-layer coatings
for the purpose of providing the beneficial operating
characteristics of each of the individual coating layers. That is,
the prior art cutting inserts having an exterior layer of Al.sub.2
O.sub.3 are designed to provide the cutting characteristics of the
Al.sub.2 O.sub.3 coated insert only, the underlying coating layers
being provided merely as barriers between the oxide layer and the
carbide substrate.
A novel coating procedure has now been discovered which allows the
secure bonding of TiC, and/or TiN onto an Al.sub.2 O.sub.3 coated
carbide cutting tool, thereby providing TiC and/or TiN as exterior
coating surfaces on top of an Al.sub.2 O.sub.3 interior coating
surface. Such a cutting tool exhibits the beneficial
characteristics of TiC, TiN and Al.sub.2 O.sub.3 in
combination.
In accordance with the invention, a thin titanium oxide layer is
disposed between the ceramic and the TiN and/or TiC coating, the
titanium oxide layer functioning to increase the adherency between
the ceramic and other coatings.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, an article of
manufacture comprises
(i) A substrate having aluminum oxide on at least portions of the
surface thereof, the aluminum oxide forming a first surface;
(ii) An intermediate layer of an oxide of titanium adjacent at
least a portion of the first surface; and
(iii) An outer layer of at least one of titanium nitride, titanium
carbide and titanium carbonitride adjacent at least a portion of
the intermediate layer.
The substrate may be either a cemented carbide substrate coated
with aluminum oxide or an aluminum base solid ceramic. The
intermediate layer contains TiO and is less than or equal to
approximately 1 micron in thickness. The outer layer may include
sub-layers of titanium nitride and titanium carbide, the titanium
carbide sub-layer being disposed between and adjacent to the
titanium nitride sub-layer and intermediate layer.
In accordance with a second aspect of the invention, a process for
coating at least portions of a substrate having a aluminum oxide on
at least portions of the surface thereof with an outer layer of at
least one of titanium carbide, titanium nitride and titanium
carbonitride, includes depositing a layer of TiO.sub.2 on the
substrate adjacent the aluminum oxide. The TiO.sub.2 is reduced to
form a TiO intermediate layer onto which the outer layer is
deposited.
DETAILED DESCRIPTION OF THE INVENTION
Briefly, an Al.sub.2 O.sub.3 coated cutting tool insert, such as
Carboloy Grade 570, is exposed to a gaseous mixture of hydrogen,
titanium tetrachloride (TiCl.sub.4) and CO.sub.2 at a temperature
around 1050.degree.-1100.degree. C. Preliminary analysis suggests
that the oxide which forms during this step is TiO.sub.2. The
temperature is then lowered in an atmosphere of hydrogen to the
temperature required for the deposition of TiC or TiN. At this
lower temperature, the tool is then exposed to an atmosphere of
gaseous TiCl.sub.4 and hydrogen. This step, possibly together with
the subsequent deposition of the TiC or TiN, results in the
transformation of the TiO.sub.2 to a combination of TiO and
TiO.sub.2 or TiO and Ti.sub.2 O.sub.3. A strongly adherent coating
of TiN or TiC can then be produced by exposing the tool to gaseous
mixtures of hydrogen, titanium tetrachloride and nitrogen, or
hydrogen, titanium tetrachloride and methane, respectively. Since
TiN and TiC can be easily bonded to each other, it is also possible
to obtain a tri-layer coating consisting of Al.sub.2 O.sub.3 , TiC
and TiN. The resulting structure is provided with exterior layers
of TiN and/or TiC strongly bonded to an interior layer of Al.sub.2
O.sub.3.
More specifically, an Al.sub.2 O.sub.3 coated carbide cutting tool
insert or Al.sub.2 O.sub.3 base solid ceramic is placed inside a
standard CVD furnace held at a temperature of about 1050.degree. C.
A gaseous mixture of hydrogen and titanium tetrachloride is passed
over the surface of the insert for up to five minutes. Titanium,
obtained by the reaction
will "activate" the Al.sub.2 O.sub.3 surface, perhaps by reacting
with the oxygen in the Al.sub.2 O.sub.3 to form TiO or
TiO.sub.2.
Next, up to 15% by volume of CO.sub.2 along with hydrogen and
titanium tetrachloride is introduced into the furnace to form a
thin layer, less than or equal to one micron, of TiO.sub.2
according to the reaction.
This step takes from 1-35 minutes, longer exposure times yielding
greater TiO.sub.2 thicknesses.
The TiO.sub.2 is subsequently reduced to TiO by lowering the
temperature to about 1000.degree. C., turning off the CO.sub.2 and
passing only hydrogen and titanium tetrachloride over the surface,
yielding the reaction
This step takes up to 30 minutes depending on the amount of
TiO.sub.2 present.
A final layer of TiN, TiC or TiCN, or a combination of any of
these, can then be deposited in a standard fashion by introducing
nitrogen, methane, or both, respectively, along with the hydrogen
and titanium tetrachloride. The result of this process is a
multi-layered coated product containing TiN or TiC, or both, on an
aluminum oxide coated insert or an aluminum oxide base solid
ceramic.
EXAMPLE
Coating a substrate with TiC using an intermediate layer of TiO was
done in a laboratory chemical vapor deposition furnace having a
reactor chamber constructed of steel. The substrate was an aluminum
oxide-coated WC-TiC-TaC-Co cemented carbide (Carboloy Grade 570).
The substrate was first cleaned inside the furnace by flowing
hydrogen gas over the substrate, which was heated to 1100.degree.
C., at a flow rate of 400 ml/min. for 10 minutes. Subsequently a
gas mixture of 10% CO.sub.2, 3% TiCl.sub.4, and 87% H.sub.2 at a
flow rate of approximately 450 ml/min. was used to deposit a
titanium oxide which was believed to be TiO.sub.2. The temperature
was held at 1100.degree. C. and 35 minutes were allowed for this
step. The titanium oxide was then partially reduced by flowing a
gas mixture of 3% TiCl.sub.4 and 97% H.sub.2 over the insert for 10
minutes at a temperature of 1035.degree. C.
A TiC coating was then deposited at 1035.degree. C. by introducing
a gas mixture of 3% CH.sub.4, 3% TiCl.sub.4, and 94% H.sub.2, for
50 minutes at a flow rate of about 450 ml/min. All of the above
steps were accomplished at atmospheric pressure.
After coating, the adhesion of the TiC layer was determined by
scratching it with a 4 kg loaded diamond. The TiC did not spall
and, in fact, rode over the top of the TiC layer. When a TiC
coating of identical thickness was deposited directly on an
aluminum oxide-coated insert (Carboloy Grade 570) without a
titanium oxide interlayer, the TiC coating was nonadherent. The
coating spalled badly, not only when scratched with a 4 kg loaded
diamond but also when scratched with a 2 kg loaded diamond.
When the TiC-coated product having the titanium oxide interlayer
was examined metallographically, it was found that the interlayer
was yellow, consistent with the presence of TiO, and 1/2-1 micron
thick. The TiC coating was 4 microns thick. It may be found that
some of the TiO.sub.2 has not been fully reduced to TiO during
reaction (3). However, as long as TiO exists adjacent to the TiN,
TiC or TiCN, and between the Al.sub.2 O.sub.3 and the TiO.sub.2,
adhesion will not be decreased.
Many variations will suggest themselves to those skilled in this
art in light of the above detailed description. All such obvious
variations are within the full intended scope of the invention as
defined by the following claims.
* * * * *